Electrical conductivity measurements on gel grown KDP crystals added with urea and thiourea

Pure and impurity added (with urea and thiourea) KDP single crystals were grown by the gel method using silica gels. Electrical conductivity measurements were carried out along both the unique axis and perpendicular directions at various temperatures ranging from 30 to 140‡ C by the conventional two-probe method. The present study shows that the conductivity in KDP crystals, for both the impurities considered, increases with the increase in impurity concentration and temperature. Activation energies were also determined and reported.     

D.C. electrical conductivity measurements on ADP single crystals added with simple organic compounds

Pure and impurity added (with urea and thiourea) ADP single crystals were grown by the free evaporation method. D.C. electrical conductivity measurements were carried out along both the unique axis and perpendicular directions at various temperatures ranging from 40–150°C by the conventional two-probe method. Activation energies were also determined. The present study indicates that the conductivity increases with the increase in impurity concentration and temperature.     

Ion transport in Au<Superscript>+</Superscript> doped/undoped KDP crystals with KI/NaI as additives

Undoped KDP and KDP crystals containing KI/NaI with/without gold doping were grown by slow evaporation technique. All the grown crystals were γ-irradiated using⁶⁰Co source. Electrical conductivity measurements were carried out on all these crystals perpendicular to the unique direction before and after y-irradiation. The present results show that the conductivity of KDP crystals increases with the addition of KI/NaI and with gold doping as well as upon rise in temperature. Computed values of activation energies from the conductivity measurements are given. For all the grown crystals, dielectric constant is measured as a function of frequency.     

Morphological aspects of some symmetrical ammonium hydrogen tartrate crystals grown by silica gel technique

Ammonium hydrogen tartrate single crystals have been prepared by the reaction of NH₄Cl and tartaric acid in silica gel. The morphology of some as-grown symmetrical crystals has been studied by optical microscopy. The growth morphology studies indicate that the grown crystals are needle-shaped, orthorhombic disphenoidal and tetrahedral disphenoidal. The growth mechanism has been assessed.     

Studies on Ce2(C2O4)3·nH2O crystals grown in hydro-silica gel

Single crystals of cerium oxalate are grown by the gel method. Ce(NO₃)₃ is allowed to diffuse into a gel in which oxalic acid is incorporated. Cerium oxalate crystals are formed by chemical reaction and the growth process is observed. Crystals are yellow-white in colour. Morphology and size of the crystals are highly influenced by the acidity of the feed solution. With 30% HNO₃ long needle shaped, with 50% HNO₃ thin hexagonal and with 100% HNO₃, well developed crystals are obtained. Natural etch pits are observed on the grown crystals due to the presence of HNO₃. Appearance of a single, large interfacial crystal is observed for 0·5 M cerium nitrate. IR spectrum confirms the presence of water molecules and carboxylic group. X-ray diffractogram gives well defined peaks. Peaks are indexed. Unit cell dimensions are determined. Thermal analysis of the samples done using TGA and DTA show the release of water molecules (endothermic) and of CO and CO₂ (exothermic) with the rare earth oxide as stable residue.     

Etch pit observations on the habit faces of gel grown nickel molybdate crystals

The results obtained from etching experiments on the habit faces of NiMoO₄·xH₂O are described. Dilute solutions of chemical reagents such as HNO₃, CH₃COOH, NaOH, KOH are found to be the best etchants for revealing dislocation etch pits. The shape and nature of the etch pits are also described.     

Study of effect of quenching and deformation on KCl: Gd<Superscript>3+</Superscript> crystals by using conductivity measurements

The study of ionic conductivity vs reciprocal temperature of pure KCl and KCl crystal doped with 0.1, 0.3 and 0.5 mole % gadolinium has been carried out in as grown, quenched from elevated temperatures (100, 350 and 500°C) and annealed at various timings i.e. 2–3 h and deformed by different percentages. The plots exhibit three well-known regions, II, III and IV (extrinsic regions). The intrinsic region I was not observed in the plots as the conductivity measurements were taken up to 575°C. From the analysis of these plots, activation energies for the migration of cation vacancy and the association of gadolinium ion with cation vacancy in the lattice of KCl crystals are calculated. These values are compared with previously reported values. Further, an attempt is made to explain the existence of oxidation state of gadolinium ion in + 3 state rather than in + 2 state as reported earlier. The variation in conductivity with effect of concentration of impurity ion, quenching and annealing and deformation with various percentages are explained on the basis of formation of impurity vacancy dipoles, vacancy — vacancy pairs (which appear in the form of precipitation), storage of cation vacancies in the form of defects, introduction of fresh dislocations, etc.